Field of the Invention
The present invention relates to a light emitting element driving device arranged to drive a light emitting element, and a light emitting device and a vehicle using the light emitting element driving device.
Description of Related Art
FIG. 9A is a diagram illustrating a general structural example of a light emitting device including a tail lamp and a stop lamp mounted in the vehicle. The light emitting device illustrated in FIG. 9A includes switches SW1 and SW2, diodes D1 to D3, driving circuits 1 and 2, at least one light emitting element (light emitting diode in FIG. 9A) Z1, and at least one light emitting element (light emitting diode in FIG. 9A) Z2. The light emitting element Z1 is a stop lamp, and the light emitting element Z2 is a tail and stop lamp.
In a tail mode in which the tail lamp is lighted, the switch SW2 becomes ON state so that an input voltage VIN is supplied to the driving circuit 2 via the switch SW2 and the diode D3. Thus, the driving circuit 2 drives the light emitting element Z2, and the light emitting element Z2 is lighted as illustrated in FIG. 9B.
In a stop mode in which the stop lamp is lighted, the switch SW1 becomes ON state so that the input voltage VIN is supplied to the driving circuit 1 via the switch SW1 and the diode D1 and also is supplied to the driving circuit 2 via the switch SW1 and the diode D2. Thus, the driving circuit 1 drives the light emitting element Z1 while the driving circuit 2 drives the light emitting element Z2, and hence the light emitting elements Z1 and Z2 are lighted as illustrated in FIG. 9C.
Here, it is supposed that an abnormality occurs in the light emitting element Z2, and hence the light emitting element Z2 is not lighted at all when the driving circuit 2 supplies power to the light emitting element Z2. In this case, the light emitting element Z1 is lighted in the stop mode as illustrated in FIG. 9D, while none of the light emitting elements Z1 and Z2 is lighted in the tail mode as illustrated in FIG. 9E.
The tail lamp is used for informing a driver of a following vehicle that there is a preceding vehicle at night or in a bad weather such as thick fog or snowstorm. Therefore, if none of lamps positioned on the rear of the vehicle is lighted in the tail mode, it is a safety problem.
Therefore, for example, the driving circuit 2 and the light emitting element Z2 illustrated in FIG. 9A are divided into two redundant circuits of the tail and stop lamps, which include a set of a driving circuit 2A and a light emitting element Z2A, and a set of a driving circuit 2B and a light emitting element Z2B, as illustrated in FIG. 10. Thus, it is possible to avoid that none of lamps positioned on the rear of the vehicle is lighted in the tail mode. However, the structure illustrated in FIG. 10 includes more components than the structure illustrated in FIG. 9A, and hence has a problem that power consumption and cost are increased.
Further, JP-A-2004-34741 proposes a tale/stop lamp having a structure in which each of the tail lamp and the stop lamp is constituted of a plurality of circuits of LEDs so that each of the tail lamp and the stop lamp has redundancy, so as to elongate life of the LEDs by periodic lighting and to light only an unbroken LED when detecting breaking of an LED. Because each of the tail lamp and the stop lamp has redundancy in the tale/stop lamp proposed in JP-A-2004-34741, the structure has a problem that power consumption and cost are increased, similarly to the structure illustrated in FIG. 10, as it requires more components than the structure illustrated in FIG. 9A.